ARRAYS

Array Access

10.4

The

[]

 may appear as part of the type at the beginning of the declaration, or as

part of the declarator for a particular variable, or both, as in this example:

byte[] rowvector, colvector, matrix[];

This declaration is equivalent to:

byte rowvector[], colvector[], matrix[][];

Once an array object is created, its length never changes. To make an array vari 

able refer to an array of different length, a reference to a different array must be

assigned to the variable.

If an array variable

v

 has type

A[]

, where

A

 is a reference type, then

v

 can

hold a reference to an instance of any array type

B[]

, provided

B

 can be assigned

to

A

. This may result in a run time exception on a later assignment; see  10.10 for

a discussion.

10.3   Array Creation

An array is created by an array creation expression ( 15.9) or an array initializer

( 10.6).

An array creation expression specifies the element type, the number of levels

of nested arrays, and the length of the array for at least one of the levels of nesting.

The array's length is available as a final instance variable

length

.

An array initializer creates an array and provides initial values for all its com 

ponents. (Contrast this with C and C++, where it is possible for an array initializer

to specify initial values for some but not all of the components of an array.)

10.4   Array Access

A component of an array is accessed by an array access expression ( 15.12) that

consists of an expression whose value is an array reference followed by an index 

ing expression enclosed by

[

 and

]

, as in

A[i]

. All arrays are

0

 origin. An array

with length

n

 can be indexed by the integers

0

 to

n 1

.

Arrays must be indexed by

int

 values;

short

,

byte

, or

char

 values may also

be used as index values because they are subjected to unary numeric promotion

( 5.6.1) and become

int

 values. An attempt to access an array component with a

long

 index value results in a compile time error.

All array accesses are checked at run time; an attempt to use an index that is

less than zero or greater than or equal to the length of the array causes an

IndexOutOfBoundsException

to be thrown.

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